Heat-reactive switch

ABSTRACT

A heat-reactive switch includes an airtight container with a housing and a lid plate, two conductive terminal pins fixed in through-holes in the lid plate, a fixed contact point fixed on one of the conductive terminal pins, a heater connected to the other conductive terminal pin and to the lid plate, a heat-reactive plate connected to the housing internal surface, the bending direction becoming inverted at a predetermined temperature, and a mobile contact point provided at the end of the heat-reactive plate. A heating element has a plurality of serpentine portions made from a metal plate in ribbon form, disposed between the lid plate and the heat-reactive plate so as to be parallel thereto. At least two of the serpentine portions are disposed to face each other while sandwiching the conductive terminal pin. Each portion follows the inner peripheral surface of the housing and have planar portions facing each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a National Stage Entry into the United States Patent andTrademark Office from International PCT Patent Application No.PCT/JP2014/063705, having an international filing date of May 23, 2014,the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a heat-reactive switch used as aprotective device of a motor or the like.

DESCRIPTION OF RELATED ART

Conventionally, many heat-reactive switches using a heat-reactive bodysuch as bimetal have been proposed as the type of heat-reactive switchmentioned above. A configuration of such a heat-reactive switch as anexample will be described with reference to FIGS. 6 and 7. Aheat-reactive switch 101 has a metallic housing 102 and a lid plate 103.An airtight container is formed by welding and fixing the lid plate 103to an opening part of the housing 102. Through holes are provided in thelid plate 103. Metallic conductive terminal pins 104A, 104B are insertedinto the through holes. The conductive terminal pins 104A, 104B arefixed in an airtight manner by an electrical insulating material 105such as glass. A fixed contact 106 is fixed to one conductive terminalpin 104A, on the inner side of the airtight container. One end of aheater 107 as a heating member is connected to the other conductiveterminal pin 104B, on the inner side of the airtight container. Theother end of the heater is connected to the lid plate 103.

A heat-reactive plate 109 configured of bimetal or the like is connectedto the inner side of the housing 102, through a connecting body 110. Amovable contact 108 is provided on a movable end of the heat-reactiveplate 109. The heat-reactive plate 109 is formed into a shallowplate-shape, and is configured to reverse its curving direction when itreaches a predetermined operating temperature, and recover its curvingdirection when it reaches a predetermined recovery temperature. Notethat the heat-reactive plate 109 normally brings the movable contact 108into contact with the fixed contact 106, as shown in FIG. 6.

The heat-reactive switch 101 is used in an enclosed electric compressoror the like for compressing a refrigerant of an air conditioner, forexample. In this case, the heat-reactive switch 101 is arranged insidean unillustrated closed housing of the compressor, such that theconductive terminal pins 104A, 104B are connected in series with amotor. During operation of the air conditioner, an operating current ofthe electric compressor flows through the heat-reactive switch 101connected in the aforementioned manner, by the following route: theconductive terminal pin 104B—the heater 107—the lid plate 103—thehousing 102—the connecting body 110—the heat-reactive plate 109—themovable contact 108—the fixed contact 106—the conductive terminal pin104A. The current flowing in this manner heats the heater 107 and theheat-reactive plate 109 of the heat-reactive switch 101. However, acurrent flowing during normal operation of the air conditioner keeps theheat-reactive plate 109 equal to or lower than the operatingtemperature. Hence, the motor continues to be energized.

However, when rotation of the motor is somehow restricted, for example,an overcurrent several times larger than the normal operation currentflows through the motor. Hence, if left in this state, components suchas coils of the motor may be burned.

If the heating value of the heater 107 and the heat-reactive plate 109largely exceed the normal state due to the overcurrent, the temperatureof the heat-reactive plate 109 rises to the predetermined operatingtemperature, and the curving direction of the heat-reactive plate 109will be reversed. Accordingly, the movable contact 108 fixed on a tipend part of the heat-reactive plate 109 moves away from the fixedcontact 106. This releases the connection between the movable contact108 and the fixed contact 106, and interrupts the electric circuit.Thus, when a malfunction occurs in the compressor, the heat-reactiveswitch 101 releases the connection between contacts, to surely interruptenergization of the motor before coils of the motor reach a burningtemperature.

SUMMARY OF INVENTION

When an electric compressor as an object to be protected is small, forexample, its energization current is small. For this reason, a heaterand a heat-reactive plate cannot generate sufficient heat by itself inthe configuration of the conventional heat-reactive switch 101. Hence,measures need to be taken to increase the heating value of the heaterand the heat-reactive plate. However, since the kind of metals used asbimetal and tri-metal of the heat-reactive plate is limited, forexample, there is a limit to increasing the heating value by improvingmaterials of the heat-reactive plate. Another conceivable method ofincreasing the heating value is to form the heat reactive-plate thin, tothereby reduce the cross-sectional area and increase the value ofresistance. However, since a drive power for opening and closing amovable contact needs to be secured for the heat-reactive plate, thereis also a limit to forming the heat-reactive plate thin. Additionally,the kind of metal used as the material of the heater is also limited dueto the required physical characteristics such as weldability and costrequirements. Hence, there is substantially a limit to replacing thematerial of the heater with a material having high resistivity. Hence,the most effective way to increase the heating value of a heat-reactiveswitch is to reduce the cross-sectional area and stretch the overalllength of a heater.

According to a heat-reactive switch of the present invention, a heatingelement of a heater has multiple meandering portions formed of astrip-shaped metal plate, and is arranged parallel to and between a lidplate and a heat-reactive plate. The meandering portions are: arrangedsuch that at least two of the meandering portions are opposite to eachother with a conductive terminal pin interposed therebetween; eachaligned with an inner circumferential surface of a housing; and are eachbent with respect to a reference axis extending in the longitudinaldirection of the housing, so that strip-shaped flat portions face eachother.

According to the heat-reactive switch of the present invention, byapplying advantageous ideas to the shape of the heater, it is possibleto reduce the cross-sectional area and extend the overall length of theheater. Hence, the heating value of the heater can be increased.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of a heat-reactive switch of an embodiment.

FIG. 2 is a longitudinal section of the heat-reactive switch.

FIG. 3 is a cross-sectional view of the heat-reactive switch.

FIG. 4 is a perspective view of a heater.

FIG. 5 is a development of the heater.

FIG. 6 is a longitudinal section of a conventional heat-reactive switch.

FIG. 7 is a cross-sectional view of the conventional heat-reactiveswitch.

DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION

Hereinbelow, a description will be given of an embodiment of aheat-reactive switch to which the present invention is applied, withreference to the drawings. As shown in FIGS. 1 and 2, a heat-reactiveswitch 1 is an airtight container configured of a metallic housing 2 anda lid plate 3. The housing 2 is formed into a long dome shape having anopen end. The lid plate 3 is adhered in an airtight manner to the openend of the housing 2 by welding, for example. Metallic conductiveterminal pins 4A, 4B are inserted into two through holes provided in thelid plate 3. These conductive terminal pins 4A, 4B are fixed by anelectrical insulating filler such as glass. Thus, the conductiveterminal pins 4A, 4B are adhered in an airtight manner, in anelectrically insulated state.

A fixed contact 6A is fixed, through a conductive fixed contact support6B, to a part of one conductive terminal pin 4A on the inner side of theairtight container. Also, a heat-reactive plate 9 configured of bimetalor tri-metal, for example, is fixed to the inner side of the housing 2through a connecting body 10. The heat-reactive plate 9 is formed into aplate shape by drawing, and has one end connected to an inner surface ofthe housing 2 through the connecting body 10. The heat-reactive plate 9reverses its curving direction, when it reaches a predeterminedtemperature. Also, a movable contact 8 is fixed to a movable end, whichis the other end, of the heat-reactive plate 9.

When the heat-reactive plate 9 is reversed, the movable contact 8 movesaway from the fixed contact 6A. This releases a connection between themovable contact 8 and the fixed contact 6A, and interrupts an electriccircuit formed of: the conductive terminal pin 4B—a heater 7—the lidplate 3—the housing 2—the connecting body 10—the heat-reactive plate9—the movable contact 8—the fixed contact 6A—the fixed contact support6B—the conductive terminal pin 4A. Note that in a normal state where theheat-reactive plate 9 is not reversed, the movable contact 8 is incontact with the fixed contact 6A and forms the above electric circuit.Thus, the movable contact 8 opens and closes the electric circuit, bybeing driven by the heat-reactive plate 9 to come into contact with andseparate from the fixed contact 6A.

As also shown in FIG. 3, one end of the heater 7 is connected to a partof the other conductive terminal pin 4B on the inner side of theairtight container. The other end of the heater 7 is connected to aninner surface of the lid plate 3. The shape of the heater 7 will bedescribed with reference to FIGS. 4 and 5. The heater 7 is configured ofa metal plate having a certain resistivity and formed into a strip shapeby pressing, for example. Also, the heater 7 has meandering portions,and the meandering portions are bent. Specifically, the heater 7 isconfigured of multiple heater units including a linear portion 7A as alinear heating element, and a semicircular portion 7B as a semicircularheating element. In the heater 7, multiple heater units are alternatelyconnected, by joining the linear portion 7A of one heater unit to thesemicircular portion 7B of another heater unit. Thus, the heater 7 hasmultiple meandering portions 7C, 7D in which multiple linear portions 7Aare provided adjacent to one another with the semicircular portion 7Binterposed therebetween.

The structure of the heater 7 adopts the meandering heating element, sothat a longer electric circuit can be obtained inside a limited space.The meandering portions 7C, 7D are connected by a connection portion 7E.In this case, the connection portion 7E is a linearly extendingstrip-shaped element. Note, however, that the connection portion 7E maybe a meandering part. Additionally, fixing portions 7F, 7G are providedon both end parts of the heater 7.

The meandering portions 7C, 7D are bent with respect to predeterminedreference axes 7H shown in FIG. 5. In this case, the reference axis 7His an axis that extends in the longitudinal direction of the longdome-shaped housing 2. The reference axis 7H set in this manner is anaxis that extends in a direction perpendicular to the center axis of thelinear portion 7A, in other words, to the extending direction of thelinear portion 7A. Also, the reference axis 7H is an axis extending in adirection perpendicular to the extending direction of the connectionportion 7E, which connects the meandering portions 7C, 7D. Note that inthe meandering portion 7D, the heater unit of a part facing the fixingportion 7F includes the linear portion 7A shorter than the linearportion 7A of the other heater units.

The meandering portions 7C, 7D are bent with respect to the referenceaxes 7H, such that a first surface of both surfaces of the linearportion 7A faces the same first surface. In other words, the meanderingportions 7C, 7D are bent 180 degrees with respect to the reference axes7H. In the meandering portions 7C, 7D bent in this manner, apredetermined gap is formed between opposite planes of the first surfaceof the same linear portion 7A, that is, between surfaces on the innerside in the bent state. Additionally, the meandering portions 7C, 7D areconfigured such that the respective strip-shaped flat parts constitutingthe linear portions 7A face each other. Also, the meandering portions7C, 7D are bent such that the extending direction of the linear portion7A is perpendicular to the connection portion 7E. Then, the heater 7 isarranged inside the airtight container such that the connection portion7E is parallel to the inner surface of the lid plate 3. Accordingly, theheater 7 is arranged inside the airtight container such that theextending direction of the linear portion 7A is vertical to the innersurface of the lid plate 3.

By bending the meandering portions 7C, 7D in this manner, it is possibleto reduce the dimension of the heater 7 in the width direction, which isthe direction perpendicular to the reference axis 7H and the extendingdirection of the connection portion 7E. Hence, the heater 7 can beaccommodated in a smaller space, and the heater 7 having a longeroverall length can be arranged inside a conventional-sized airtightcontainer. Also, the heater 7 having the meandering portions 7C, 7D bentin this manner is arranged inside the airtight container, such that thelinear portion 7A of one meandering portion 7C faces the linear portion7A of the other meandering portion 7D. Additionally, the heater 7 isarranged inside the airtight container, such that the linear portion 7Aof one meandering portion 7C is parallel to the linear portion 7A of theother meandering portion 7D.

Also, when arranged inside the airtight container, the heater 7surrounds the periphery of the conductive terminal pin 4B with thefixing portion 7G—the meandering portion 7C—the connection portion7E—the meandering portion 7D—the fixing portion 7F. That is, the heater7 is arranged around the conductive terminal pin 4B, in such a manner asto form a spiral. Additionally, the heater 7 is arranged such that themeandering portions 7C, 7D are opposite to each other with theconductive terminal pin 4B interposed therebetween. Also, the heater 7is arranged such that the meandering portions 7C, 7D are parallel to theinner surface of the lid plate 3. The heater 7 is also arranged suchthat lateral surfaces on the outer sides of the meandering portions 7C,7D are aligned with an inner circumferential surface of the housing 2.Then, the fixing portion 7G as an end part of the heater 7 on thecircumferential edge side is fixed to the inner surface of the lid plate3 by welding, for example. Meanwhile, the fixing portion 7F as an endpart of the heater on the center side is fixed to an end part of theconductive terminal pin 4B inside the airtight container, by welding,for example.

Moreover, the heater 7 is arranged inside the airtight container suchthat the connection portion 7E is on the heat-reactive plate 9 side, abent portion closest to the connection portion 7E is on the lid plate 3side, and the next bent portion is on the heat-reactive plate 9 side.Hence, when the heater 7 is arranged inside the airtight container, itsarea is larger on the heat-reactive plate 9 side than on the lid plate 3side opposite to the heat-reactive plate 9 side.

According to the heat-reactive switch 1, the heater element of theheater 7 has multiple meandering portions 7C, 7D formed of astrip-shaped metal plate. These meandering portions 7C, 7D are arrangedparallel to at least the lid plate 3, between the lid plate 3 and theheat-reactive plate 9. Also, the meandering portions 7C, 7D are arrangedopposite to each other with the conductive terminal pin 4B interposedtherebetween. Also, each of the meandering portions 7C, 7D is alignedwith the inner circumferential surface of the housing 2. Also, themeandering portions 7C, 7D are partially bent with respect to thereference axes 7H extending in the longitudinal direction of the housing2. The meandering portions 7C, 7D are also configured such that theirstrip-shaped flat portions are opposite to each other. That is,according to the heat-reactive switch 1, by applying advantageous ideasto the shape of the heater 7, it is possible to reduce thecross-sectional area and extend the overall length of the heater 7.Hence, the heating value of the heater 7 can be increased.

In a deployed state, a heater formed into a strip shape is likely toreceive force in a direction perpendicular to the surface of the heater,and therefore may easily warp. However, according to the heat-reactiveswitch 1 to which the present invention is applied, the meanderingportions 7C, 7D as heating elements are bent with respect to thepredetermined reference axes 7H. Additionally, the meandering portions7C, 7D are bent with respect to the predetermined reference axes 7H,such that the extending direction of the linear portion 7A is verticalto the inner surface of the lid plate 3. Hence, force is less likely tobe applied perpendicularly on the surfaces of the meandering portions7C, 7D, and warpage resistance of the heater 7 can be improved.

Also, when vibration or impact is applied, a large stress acts on afixing portion for fixing the heater. In particular, a configuration inwhich a heater projects largely in the lateral direction tends to beaffected by vibration, since the center of gravity of the heater isseparated from the fixing portion. Hence, when vibration or impact isapplied, a large rotary torque acts on the fixing portion, anddurability thereof is degraded. However, according to the heat-reactiveswitch 1 to which the present invention is applied, the heater 7 ispartially bent, and therefore does not largely project in the lateraldirection. Also, the heater 7 is arranged in such a manner as to form aspiral parallel to the lid plate 3, and its fixing portion 7F on thecenter side is fixed to the conductive terminal pin 4B. According tothis configuration, the fixing portion 7F is positioned close to thecenter of gravity of the heater 7. Hence, even when vibration or impactis applied, the fixing portion 7F is less likely to receive an excessiverotary torque.

Also, the heater 7 is formed into a spiral as a whole, and the fixingportions 7F, 7G on both end parts are arranged at a predeterminedinterval in the longitudinal direction of the heat-reactive switch 1. Inother words, the heater 7 has an asymmetrical shape as a whole. Inaddition, since the heater 7 has the meandering portions 7C, 7D asheating elements bent in a complex manner, lengths and directions of theparts are varied in many ways. This can suppress occurrence of resonancephenomena in the heater 7 due to vibration or the like.

Note that the present invention is not limited only to the singleembodiment described above, and various modifications or extensions canbe made without departing from the gist of the invention. For example,the number of meandering portions of the heater is not limited to two,and may be varied as appropriate.

The invention claimed is:
 1. A heat-reactive switch, comprising: anairtight container formed by adhering a lid plate in an airtight mannerto an open end of a metallic, long, dome-shaped housing; first andsecond conductive terminal pins respectively inserted into first andsecond through holes in the lid plate, wherein each of the first andsecond conductive terminal pins are fixed in an airtight manner by anelectrical insulating filler; a fixed contact fixed to the firstconductive terminal pin inside the airtight container; a heater having afirst end connected to the second conductive terminal pin and a secondend connected to the lid plate inside the airtight container; aheat-reactive plate having a first end connected to an inner surface ofthe housing, wherein a curving direction of the heat-reactive plate isreversed at a predetermined temperature; and a movable contact providedon a second end of the heat-reactive plate and constituting a pair ofswitching contacts with the fixed contact, wherein: a heating element ofthe heater has a plurality of meandering portions formed of astrip-shaped metal plate and is arranged parallel to and between the lidplate and the heat-reactive plate; and the meandering portions arearranged such that at least two of the meandering portions are oppositeto each other with the second conductive terminal pin interposedtherebetween, each aligned with an inner circumferential surface of thehousing, each bent with respect to two reference axes extending in thelongitudinal direction of the housing, so that first surfaces of themeandering portions face each other, and each of the meandering portionsis bent twice with respect to the two reference axes, respectively. 2.The heat-reactive switch according to claim 1, wherein the meanderingportions are formed by alternately connecting a plurality of heaterunits, each including a linear portion and a semicircular portion. 3.The heat-reactive switch according to claim 2, wherein the meanderingportions are bent such that adjacent linear portions define firstsurfaces that face one another.
 4. The heat-reactive switch according toclaim 2, wherein the meandering portions are bent such that an extendingdirection of the linear portion is vertical to an inner surface of thelid plate.
 5. The heat-reactive switch according to claim 2, wherein afirst linear portion is arranged parallel to a second linear portion. 6.The heat-reactive switch according to claim 1, wherein the heater has afirst end part on a circumferential edge side fixed to the lid plate anda second end part on a center side fixed to the second conductiveterminal pin.